1. Field of the Invention
This invention relates to a data transmission system which encodes and transmits image information by using facsimile apparatus or other similar information transmission equipment.
2. Description of the Prior Art
In general, the Group 3 facsimile apparatus for document transmission are designed to transmit image information in accordance with the control procedure and the transmitting method stipulated in CCITT (International Telegraph and Telephone Consultative Committee) Recommendations T.30 and T.4. Recommendation T.4 of the CCITT stipulates the minimum transmission time of a total coded scan line (hereinafter called a line). In fact, the minimum transmission time of one line should conform to the standard of 20 milliseconds with other times such as 10 milliseconds and 5 milliseconds also approved as options.
The identification and choice of this minimum transmission time are communicated between the transmitting and receiving facsimile apparatus by the premessage procedure which conforms to the control procedure of CCITT Recommendation T.30.
The minimum transmission time is chiefly determined by the recording speed and the code buffer capacity which stores transmitted codes of the facsimile apparatus on the receiving side. In general, the facsimile apparatus internally holds such information.
A line of image information is composed of a series of variable length code words. Each code word represents a run length of either all white or all black. White runs and black runs alternate. The end-of-line (hereinafter called EOL) code word is inserted between data code words which correspond to the image information in a line and data code words which correspond to the image information in the next line. This EOL code word is added before data code words. In the event that the time required for transmitting the above-mentioned data code words and the EOL code word is less than the minimum transmission time, a Fill code word is added after the data code words. This ensures that a line with a small quantity of data code words has its transmission time extended beyond the minimum transmission time.
FIG. 3 shows the relationship of such code words. FIG. 3(1) explains the relationship among the transmitted code words which correspond to the first several lines of a manuscript image to be transmitted and FIG. 3(2) explains the relationship among the transmitted code words which correspond to the last line on the first page. The minimum transmission time .DELTA.T per encoded line is determined by the pre-message procedure between the facsimile apparatus on the transmitting side and the receiving side. After the pre-message procedure including determination of the minimum transmission time .DELTA.T, etc., image information of the first line is transmitted. The transmitted code words of the first line consist of the EOL code word and the data code words D1. For example, the time .DELTA.T1 required for transmitting the code words of the first line is longer than the minimum transmission time .DELTA.T. The transmitted code words of the second line consist of the EOL code word, the data code words D2 and the Fill code word which represents nul information. The time .DELTA.T2a required for transmitting the EOL code word and the data code word D2 is shorter than the minimum transmission time .DELTA.T. Therefore, the Fill code word is added. In this way, the time .DELTA.T2 required for transmitting the code words of the second line is at least as long as or longer than the minimum transmission time .DELTA.T.
As described above, in the event that the time required for transmitting the data code words and the EOL code word of a line is shorter than the minimum transmission time .DELTA.T, the Fill code word is added to make the above-mentioned time at least as long as or longer than the minimum transmission time .DELTA.T as in the aforementioned second line.
Six EOL code words are normally added after the data code words of the last line on a page. The end of a document transmission is signified by sending six consecutive EOLs (the RTC signal) to the receiving facsimile apparatus. Following the RTC signal, the post-message procedure starts.
In the data transmission system as mentioned above, the Fill code word is inserted when there are only a few data words on a line and the time required for transmitting the EOL code word and the data code words is shorter than the minimum transmission time .DELTA.T. This Fill code word does not result in the transmission of any actual image and, as explained above, is inserted for the purpose of making the time required for transmitting a line as long as or longer than the minimum transmission time .DELTA.T. However, the time required for transmitting the total manuscript image is nevertheless made longer by this method.
The facsimile apparatus disclosed in the Japanese Published Unexamined Patent Application No. SH056(1981)-43863 has a memory which stores the destination numbers of terminal locations and the specific parameters necessary to communicate with those terminals, and a means to judge whether or not the communication parameters of the destination number are stored when the number is input. As shown in the Japanese Published Unexamined Patent Application No. SHO53(1978)-122312, even if the Fill code word is added to data code words in the decoding circuit of the variable length code words, such facsimile apparatus as is able to securely detect the EOL code word in the same circuit is known. However, the above-mentioned problem can not be solved with these facsimile apparatus.
It is an object of the present invention to provide a data transmission system by which data transmitting speed is remarkably improved, minimizing the transmission of nul information which is normally inserted to make the time required for transmitting one unit data as long as or longer than the minimum transmission time in a data transmission system in which the minimum transmission time is set in accordance with the processing speed and other conditions of equipment specific to the receiving side apparatus.